1. Field of the Invention
The present invention relates to a tire inspection system including apparatus and methods for inspecting the integrity of tires through the use of penetrative emanation, such as X-radiation.
2. Background Terminology
Several terms of art are commonly used in conjunction with tires. The outer diameter or "O.D" of a tire is measured to an outer wear surface known as the tire "tread", even though it may be a smooth surface. The annular sides of a tire are called "sidewalls". The inner diameter or "I.D." of a tire is measured to sidewall portions called "beads". The axis about which a tire is intended to rotate, i.e., the axis common to both tire beads, is called the "central axis". A plane which extends perpendicular to the central axis and intersects the center of the tire tread is called the "central plane". The open space inside a tire and radially outwardly of the beads is called the "tire torus". The open space inside a tire which includes the torus and the space radially inwardly of the beads is called the "tire annulus". The distance from the outer surface of one sidewall to the outer surface of the other sidewall is called the "width" of the tire.
3. Prior Art
A number of proposals have been made for inspecting tires with X-rays and other penetrative emanation. Inspection with X-radiation has advantages over other known tire inspection methods, in that it provides information about the internal structure or integrity of a tire including a clear indication of whether internal components such as steel belts and the like are properly positioned and intact.
In the past, X-ray tire inspectors were used primarily as laboratory tools. Little use was made of X-ray inspection equipment on high rate production lines for a number of reasons including:
1. The inspection system was a relatively expensive piece of apparatus;
2. The apparatus could only inspect a limited number of tires from a production run due to its relatively slow operation;
3. A significant amount of tire handling and manipulation was typically required to position a tire in the apparatus for inspection; and,
4. After a tire was positioned for inspection, the apparatus was not capable of inspecting the total tire from bead to bead, without requiring that the tire be repositioned one or more times for successive inspection runs.
In view of these disadvantages, X-ray inspection of production tires was typically used either to inspect only selected portions of tires randomly sampled from a production run, or to inspect special duty tires such as are used on aircraft and on heavy duty, off-highway road equipment.
With the recent increased emphasis on vehicle safety, and the advent of steel belted tires, the need for X-ray inspection of all tires from a production run has become apparent. A number of proposals have been made to improve X-ray inspection apparatus, providing a capability to handle a large volume of tires of the same size from a production run.
A significant advance was made in tire inspection capability with the introduction of a rotatable X-ray tube, as described in the referenced Tire Inspector Patent. The rotatable tube permitted the complete inspection of a tire from bead to bead without requiring any reorientation of the tire or tube. With the tube located at a single position within or near the tire beads and with the tire rotating about its central axis, the tube is positioned to inspect one tire bead and is then scanned through a full arc inspecting tread, sidewalls and the other tire bead.
Still another advance was made with the introduction of a tire inspector having multiple-function tire supporting spindles, as described in the reference Tire Handling Patent. Two sets of spindles carried on separate carriages are inserted into the annulus of a tire to be inspected. The sets of spindles enter the tire axially from opposite sides. Once the spindles have entered the annulus, they move in directions parallel to the central plane to engage the tire beads. While the spindles continue to engage the tire beads, they are operable to support beads of the tire axially away from each other as may be required to facilitate inspection. The use of multi-function spindles has greatly simplified the manipulation of tires for inspection.
Despite the fact that several advances have been made in X-ray tire inspection, little has been done to satisfy the need for an X-ray tire inspector which is capable of efficiently, automatically and safely inspecting tires of a wide range of admixed sizes. Prior art inspection apparatus has not been well adapted to sequentially inspect tires of mixed sizes, and accordingly has not met the needs of a number of tire manufacturers whose production includes an admixture of tire sizes.
A recent proposal has suggested the use of a tire size sensing system for measuring tire O.D. and width before a tire is admitted to an enclosure for X-ray inspection. Once the measured tire has entered the enclosure which surrounds the X-ray inspection system, the tire tread is engaged by rotatable spools and is elevated to position its central plane in alignment with the center of the screen of an X-ray imaging system. An X-ray tube is then swung upwardly into the tire annulus and turned on to initiate the inspection. Inspection continues as the tire is rotated by the spools. The X-ray tube and the imaging system are mechanically coupled together so that both can be pivoted upwardly and downwardly to inspect the tire sidewalls.
This recent proposal has a number of disadvantages. Positioning of the tire for inspection continues to require a substantial amount of step-by-step tire manipulation. The tire is first engaged by spools. The tire is then elevated by the spools to an inspection level. Beadspreaders are then inserted into one side of the tire torus and extended to spread the tire bead. Each of these steps must be performed in sequence, it being necessary for the tire to be raised into position before the beads can be spread. When these steps are completed, the X-ray tube is then swung into position from below.
Another disadvantage with this recent proposal is that X-ray tube operation must be terminated between tire inspections. Repeatedly energizing and de-energizing the tube and its associated generator equipment may add to the required inspection time and may also diminish the operating life of the X-ray tube.
Another disadvantage of previously proposed X-ray tire inspection apparatuses is their inflexibility of operation. While computers have been used to some extent to facilitate and speed up the operation of the apparatus, no use has been made of a programmable computer system to permit inspection cycles to be widely varied by altering the program, without the need for mechanical changes in the apparatus.
Still another disadvantage of prior proposed inspection apparatuses is that their several movable components are not independently operable and do not utilize servo-system technology to permit their operation to be controlled and monitored from a central control console. No thorough system of malfunction analysis has been provided on known tire inspectors.
The use which is made of computer systems in prior proposals includes the storage of sensed tire size data, and the subsequent control of the apparatus to inspect a tire of the sensed size. The computer is operated in an "open loop" fashion. Command signals are issued by the computer to components of the apparatus. If the components respond as intended, a proper inspection sequence is carried out.
The "open loop" mode of operation has several disadvantages. While the computer issues commands, it has no knowledge of whether the commands are properly executed. The computer cannot sense the conditions and positions of the components it commands and this makes it difficult to prevent the occurrence of potentially destructive or dangerous conditions. If the computer issues a defective command or if the apparatus improperly executed a command, potentially destructive or dangerous conditions can easily arise.
Still another disadvantage of "open loop" operation is that no use can be made of the computer to assist in analyzing a malfunction. When a defect arises, it is often difficult to diagnose, and substantial machine "down time" may result before the malfunction is analyzed and corrected.
Still another drawback of the proposed use of "open loop" computer control systems in tire inspectors is the failure of such systems to provide for human intervention in the inspection procedure. The operator cannot interrupt the procedure to change its sequence, or to skip certain steps, or to add certain steps, or to lengthen or shorten certain steps. The versatility of these proposed systems leaves much to be desired.